The present invention relates to a process for producing an L-amino acid by fermentation. An aliphatic amino acid such as L-valine, L-leucine and L-isoleucine is an essential nutrient for humans and animals, and is employed in pharmaceuticals, foods and animal feeds.
Various processes for producing an L-amino acid by direct fermentation are known. As a process for producing L-valine, processes using microorganisms belonging to the genus Serratia, Corynebacterium and Arthrobacter are known. As a process for producing L-valine using a microorganism belonging to the genus Escherichia, a process using a microorganism having resistant to .beta.-hydroxyisoleucine, .beta.-2-thienylalanine or 1,2,4-triazolalanine is known (Japanese Published Unexamined Patent Application No. 51989/81).
As a process for producing L-leucine, processes using microorganisms belonging to the genus Serratia, Corynebacterium and Arthrobactor are known. As a process for producing L-leucine using a microorganism belonging to the genus Escherichia, a process using a microorganism having resistance to .beta.-2-thienylalanine is known (Japanese Published Unexamined Patent Application No. 72695/81). As a process for producing L-isoleucine, processes using microorganisms of Serratia, Corynebacterium and Arthrobactor are known. As a process for producing L-isoleucine using a microorganism belonging to the genus Escherichia, a process using a microorganism having resistance to isoleucine analogues is known (EP-A-0542487).
However, there has not been known a process for producing aliphatic amino acids using microorganisms having resistance to 2-ketobutyric acid.